1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for creating an annular barrier in a wellbore. More particularly, embodiments of the invention relates to methods and apparatus for isolating at least a portion of a wellbore from at least another portion of the wellbore.
2. Description of the Related Art
As part of the wellbore construction process, a hole or wellbore is typically drilled into the earth and then lined with a casing or liner. Sections of casing or liner are threaded together or otherwise connected as they are run into the wellbore to form what is referred to as a “string.” Such casing typically comprises a steel tubular good or “pipe” having an outer diameter that is smaller than the inner diameter of the wellbore. Because of the differences in those diameters, an annular area occurs between the inner diameter of the wellbore and the outer diameter of the casing and absent anything else, wellbore fluids and earth formation fluids are free to migrate lengthwise along the wellbore in that annular area.
Wells are typically constructed in stages. Initially a hole is drilled in the earth to a depth at which earth cave-in or wellbore fluid control become potential issues. At that point, drilling is stopped and casing is placed in the wellbore. While the casing may structurally prevent cave-in, it will not prevent fluid migration along a length of the well in the annulus. For that reason, the casing is typically cemented in place. To accomplish that, a cement slurry is pumped down through the casing and out the bottom of the casing. Drilling fluid, water, or other suitable wellbore fluid is pumped behind the cement slurry in order to displace the cement slurry into the annulus. Typically, drillable wiper plugs are used to separate the cement from the wellbore fluid in advance of the cement volume and behind it. The cement is left to cure in the annulus thereby forming a barrier to fluid migration within the annulus. After the cement has cured, the cured cement remaining in the interior of the casing is drilled out and the cement seal or barrier between the casing and the formation is pressure tested. If the pressure test is successful, a drill bit is then run through the cemented casing and drilling is commenced from the bottom of that casing. A new length of hole is then drilled, cased, and cemented. Depending on the total length of well, several stages may be drilled and cased as described.
As previously mentioned, the cement barrier is tested between each construction stage to ensure that a fluid tight annular seal has been achieved. Typically, the barrier test is performed by applying pressure to the casing internally, which typically involves pumping fluid into the casing string from the surface. The pressure exits the bottom of the casing and bears on the annular cement barrier. The pressure is then monitored at the surface for leakage. Such testing is often referred to as a “shoe test” where the word “shoe” indicates the lowermost portion or bottom of a given casing string. When another well section is needed below a previously cased section, it is important that a successful shoe test be completed before progressing with the drilling operation.
Unfortunately, cementing operations require cessation of drilling operations for considerable periods of time. Time is required to mix the cement and then to pump it downhole. Additional time is required to allow the cement to cure once it is in place. During the cementing operations drilling rig costs and other fixed costs still accrue yet no drilling progress is made. Well construction is typically measured in feet per day. Fixed costs such as the drilling rig costs, which are charged on a per day basis, are translated to dollars per foot. Because cementing takes time with zero feet drilled, the cementing operation merely increases the dollar per foot metric. Therefore, it is beneficial to minimize or eliminate such “zero feet drilled” steps in order to decrease the average dollar per foot calculation associated with well construction costs.
Expandable wellbore pipe has been used for a variety of well construction purposes. Such expandable pipe is typically expanded mechanically by means of some type of swage or roller device. An example of expandable casing is shown in U.S. Pat. No. 5,348,095, which is incorporated by reference herein in its entirety. Such expandable casing has been described in some embodiments as providing an annular fluid barrier when incorporated as part of a casing string.
Expandable pipe has also been shown having non-circular (“folded”) pre-expanded cross-sections. Such initially non-circular pipe is shown to assume a substantially circular cross-section upon expansion. Such pipe may have substantially the same cross-sectional perimeter before and after expansion, i.e., where the expansion comprises a mere “unfolding” of the cross-section. Other such pipe has been shown wherein the cross-section is “unfolded” and its perimeter increased during the expansion process. Such non-circular pipes can be expanded mechanically or by application of internal pressure or by a combination of the two. An example of “folded” expandable pipe is shown in U.S. Pat. No. 5,083,608, which is incorporated by reference herein in its entirety.
As mentioned above, mechanical pipe expansion mechanisms include swage devices and roller devices. An example of a swage type expander device is shown in U.S. Pat. No. 5,348,095, which is incorporated by reference herein in its entirety. An example of a roller type expander device is shown in U.S. Pat. No. 6,457,532, which patent is incorporated by reference herein in its entirety. U.S. Pat. No. 6,457,532 also shows a roller type expander having compliant characteristics that allow it to “form fit” an expandable pipe to an irregular surrounding surface such as that formed by a wellbore. Such form fitting ensures better sealing characteristics between the outer surface of the pipe and the surrounding surface.
Expandable pipe has been shown and described having various exterior coatings or elements thereon to augment any annular fluid barrier created by the pipe. Elastomeric elements have been described for performing such function. Coated expandable pipe is shown in U.S. Pat. No. 6,789,622 and that patent is incorporated by reference herein in its entirety.
Regardless of whether or not the cross-section is initially circular or is folded, expandable pipe has limitations of expandability based on the expansion mechanism chosen. When expandable pipe is deployed for the purpose of creating an annular fluid barrier, the initial configuration of the pipe and the expansion mechanism used must be carefully tailored to a given application to ensure that the expansion is sufficient to create a barrier. If the chosen expansion mechanism is miscalculated in a given circumstance, the result can be extremely disadvantageous. In such a situation, the expanded pipe is not useful as a barrier and further, because the pipe has been expanded or partially expanded, retrieval may be impractical. Remedying such a situation consumes valuable rig time and accrues other costs associated with remediation equipment and replacement of the failed expandable pipe.
Therefore, a need exists for improved methods and apparatus for creating an annular barrier proximate a casing shoe that eliminates the necessity for cementing. There further exists a need for improved methods and apparatus for creating an annular fluid barrier using expandable pipe that provides for a successful recovery from a failed expansion attempt.